Ultraviolet Spectroscopic Detection of Nitrate and Nitrite in Seawater Simultaneously Based on Partial Least Squares

Abstract

A direct, reagent-free, ultraviolet spectroscopic method for the simultaneous determination of nitrate (NO3−), nitrite (NO2−), and salinity in seawater is presented. The method is based on measuring the absorption spectra of the raw seawater range of 200–300 nm, combined with partial least squares (PLS) regression for resolving the spectral overlapping of NO3−, NO2−, and sea salt (or salinity). The interference from chromophoric dissolved organic matter (CDOM) UV absorbance was reduced according to its exponential relationship between 275 and 295 nm. The results of the cross-validation of calibration and the prediction sets were used to select the number of factors (4 for NO3−, NO2−, and salinity) and to optimize the wavelength range (215–240 nm) with a 1 nm wavelength interval. The linear relationship between the predicted and the actual values of NO3−, NO2−, salinity, and the recovery of spiked water samples suggest that the proposed PLS model can be a valuable alternative method to the wet chemical methods. Due to its simplicity and fast response, the proposed PLS model can be used as an algorithm for building nitrate and nitrite sensors. The comparison study of PLS and a classic least squares (CLS) model shows both PLS and CLS can give satisfactory results for predicting NO3− and salinity. However, for NO2− in some samples, PLS is superior to CLS, which may be due to the interference from unknown substances not included in the CLS algorithm. The proposed method was applied to the analysis of NO3−, NO2−, and salinity in the Changjiang (Yangtze River) estuary water samples and the results are comparable with that determined by the colorimetric Griess assay.

Effect of Nanoparticles on the Thermal Stability and Reaction Kinetics in Ionic Nanofluids

“…Indirect methods based on UV and visible spectroscopy allow quantifying the nitrite concentration with an excellent limit of detection [ 42 , 43 ]. The UV-Vis absorption spectra were performed to NaNO 3 /NaNO 2 mixtures samples for 0.3 M (in deionized water) at 2.5%, 5%, 12.5% and 25% wt.…”

“…in NaNO 2 concentration , Figure 3 . The characteristic absorption peaks for [ and [ ions were found at 354 nm and 300 nm, respectively [ 43 , 44 ]. The most interesting result is the increase observed in the nitrite peak as the concentration increases from 2.5% to 25% wt., Figure 3 a.…”

Applications of Online UV-Vis Spectrophotometer for Drinking Water Quality Monitoring and Process Control: A Review

“…PLS regression is a commonly used method to remove the particle's effect on the measurements of water quality parameters based on the multiple wavelength spectra. It has been used to remove the particle's effect on the water quality multi-parameter, such as COD in artificial seawater [62], suspended solid in brackish water [56], COD in lake water [63], COD and TOC in seawater [54] and stream water [17], nitrate in water [53], nitrate and nitrite in seawater [64], DOC in surface water [57] and drinking water [52] and ozone in drinking water [55].…”

Industry Partnership: Lab on Chip Chemical Sensor Technology for Ocean Observing

“…Optical (direct spectrophotometry of seawater) sensors (Finch et al, 1998;Johnson and Coletti, 2002) offer reagent free, high frequency and low energy per measurement data, are commercially available (e.g., SUNA v2, Seabird Scientific, United States), robust and deployable on the small platforms such as profiling floats (Johnson et al, 2010). Whilst they currently only measure nitrate operationally, they could also access nitrite (Wang et al, 2021) using spectral chemometrics and with the addition of acid titration can also measure [CO 3…”

“…2− ] ( Martz et al, 2009). However, they are prone to interference from overlapping absorption spectra of other natural water constituents, biofouling and calibration drift (Sakamoto et al, 2009;Wang et al, 2021) and are less accurate/precise (2 µM/0.3 µM; Suna V2, Seabird Scientific, United States) than traditional nutrient analysis (0.1/0.1 µM; Hydes et al, 2010;Becker et al, 2020).…”